Problem: Gabriela is 3 times as old as Jessica and is also 8 years older than Jessica. How old is Gabriela?
Explanation: We can use the given information to write down two equations that describe the ages of Gabriela and Jessica. Let Gabriela's current age be $g$ and Jessica's current age be $j$ $g = 3j$ $g = j + 8$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $g$ is to solve the second equation for $j$ and substitute that value into the first equation. Solving our second equation for $j$ , we get: $j = g - 8$ . Substituting this into our first equation, we get the equation: $g = 3$ $(g - 8)$ which combines the information about $g$ from both of our original equations. Simplifying the right side of this equation, we get: $g = 3g - 24$ Solving for $g$ , we get: $2 g = 24$ $g = 12$.